Necessity of performing transformation work on an image is notable in a situation such that advertising effect of a poster, etc. must be heightened or that impression of an image must be exalted.
In response to such requirements, conventionally a method as disclosed in Japanese Patent Publication No. 56-30892 is used. The method comprises steps of marking a scanning start line of an optional curve on the top edge of an original picture as well as a scanning stop line on the bottom edge of the original picture, and scanning the original picture from the start line to the end line according to the curve of the start line to obtain a transformed image of the original picture. However this procedure for marking both lines is troublesome and moreover the following malfunction might occur when the lines having specific colors are drawn on an original picture including the specific colors. That is, a scan might halt on a midway place of the original picture where the same specific color
as the stop line exists. In addition, this kind of marking work might bring rugged transformation of the original picture of its pixel level.